1. Field of the Invention
The present invention relates to a voltage regulating apparatus and a voltage regulating method and, more particularly, to a technology for controlling a drive voltage supplied to a target load.
2. Description of the Related Art
Battery-driven portable equipment such as cell phones and personal data assistants (PDA) use light-emitting diodes (LED) for a variety of purposes. For example, LEDs are used as backlight of a liquid crystal display (LCD) or an electronic flash light for a charge-coupled device (CCD) camera. LEDs emitting different colors are operated to blink for illumination. In order to drive an LED, a battery voltage of about 3.6V of, for example, a lithium ion battery should be boosted to a drive voltage of about 4.5V. When the battery voltage drops due to battery consumption, the battery voltage should be boosted by a higher step-up ratio.
Thus, in order to maintain the proper driving status of the target load such as an LED, the step-up ratio should be properly controlled in accordance with the operating environment. For example, a patent document No. 1 discloses a rear combination lamp apparatus for vehicle use that controls the step-up ratio so that a drive voltage of about 16V continues to be supplied to an LED unit comprising 8 LEDs connected in series when the battery voltage in the vehicle drops.
[Patent Document No. 1]
Japanese Published Patent Application No. 2003-187614
Some cell phones available these days comprise loads, such as a plurality of LEDs connected in parallel. The technology of the patent document No. 1 cannot be applied to such equipment. A new perspective is required in regard to the control of drive voltage supplied to loads such as a plurality of LEDs.